This application is the national phase under 35 U.S.C. xc2xa7 371 of PCT International Application No. PCT/DE01/00428 which has an International filing date of Jan. 30, 2001, which designated the United States of America and which claims priority on German Patent Application No. 100 04 833.1 filed Feb. 1, 2000, the entire contents of which are hereby incorporated by reference.
The invention generally relates to a multipole low-voltage circuit breaker having an enclosure and having one current detection device for each pole. Preferably, each current detection device includes an electrical conductor, which is associated with a switching contact system for that pole, and a secondary part through which the electrical conductor passes.
Circuit breakers of the stated type have been disclosed, for example, in U.S. Pat. No. 4,673,779 or U.S. Pat. No. D 347,623 (Design Patent) in conjunction with U.S. Pat. No. 4,497,992. The current detection devices provided therein have the object of producing a signal which is dependent on the current flowing in each of the poles and which is evaluated in an overcurrent tripping device, in order to interrupt a circuit for protection of loads and electrical systems. Since, in some circumstances, only one of the poles of a circuit breaker may be affected by a high fault current, each of the poles is equipped with a current detection device.
The secondary parts of the current detection devices generally include a mount and a winding which is fit to it and which may be a single-layer winding or a multilayer winding. Furthermore, these components are generally provided with an enclosure or a casing for protection against damage and against external influences. During the process of manufacturing a low-voltage circuit breaker, the secondary parts of the current detection devices are selected and mounted individually in accordance with the user""s requirements. Suitable recesses or pockets are provided for this purpose on the rear face of the enclosure of the circuit breakers, through which the electrical conductors which are connected to the switching contact systems extend, and at the same time form connecting devices for connection to a circuit that is to be protected.
Once the secondary parts have been pushed onto the electrical conductors, suitable sealing covers are fit to the rear face of the enclosure. This is done in order firstly to protect the secondary parts of the current detection devices, and in order secondly to support the electrical conductors on the enclosure of the circuit breaker, as close as possible to their connection point. The reason for this measure is that circuit breakers of the type mentioned are subject to extraordinarily high mechanical forces in the event of a short circuit, which can lead to damage to the circuit breaker and to the conductors continuing on from them if busbars are not adequately supported.
An embodiment of the invention includes an object of improving the current detection in multi-pole low-voltage circuit breakers, and/or of simplifying the installation of the current detection devices.
According to an embodiment of the invention, an object may be achieved in that the secondary parts of the current detection devices for all the poles of the circuit breaker are arranged in a common mounting body, which has aperture openings for the electrical conductors as well as attachment devices for detachable connection of the mounting body to the enclosure of the circuit breaker.
The combination, as envisaged according to an embodiment of the invention, of the secondary parts of the current detection devices of all the poles to form a standard assembly makes it possible to provide units, which are matched to one another and are tested together, for current detection in multi-pole circuit breakers. This reduces the time required for mechanical installation and calibration and adjustment of the completed circuit breaker. The multi-pole mounting body at the same time improves the mechanical strength, by supporting the electrical conductors in a cohesive body.
The mounting body which is provided according to an embodiment of the invention may have recesses for holding the secondary parts, with these secondary parts being mounted in the recesses by encapsulating them with a synthetic resin compound. It is thus possible to use the same materials and production methods not only for production of the mounting body but also for the attachment of the secondary parts, as those which are already known for the production of the enclosures and of enclosure parts of circuit breakers, and of the associated single-pole current detection devices.
For the purpose of an embodiment of the invention, the mounting body, which essentially has a rectangular outline and is in the form of a panel may be configured as part of a rear wall of the enclosure of the circuit breaker, with the recesses which have been mentioned being arranged on that side of the mounting body which faces the interior of the circuit breaker. This arrangement provides good protection for the secondary parts against damage during handling of the circuit breaker and has a good protective effect on the electrical conductors which are associated with the current detection devices.
As already mentioned, the current detection devices for low-voltage circuit breakers may be of widely differing types. One frequently used type is the transposed conductor current transformer, which has a nonmagnetic mount surrounding the electrical conductor and has a single-layer winding, whose start and end are directly adjacent to one another. The output variable from a current sensor such as this is, in contrast to inductive current transformers, dependent not only on the number of turns, but also on their geometrical distribution and arrangement.
According to one refinement of an embodiment of the invention, in this context, it is possible to compensate for the different transmission response of the transposed conductor current transformer resulting from manufacturing tolerances by each of the transposed conductor current transformers having an associated voltage divider, which is composed of resistors, and by these voltage dividers likewise being fit to the mounting body. The adjustment of the transposed conductor current transformers can therefore be carried out before they are installed in a circuit breaker, which represents a simplification in comparison to the previously required matching and calibration of the completed circuit breaker.
The voltage dividers which have been mentioned may each be configured such that they can be adjusted by means of an adjustment element, with all the adjustment elements being arranged in an accessible manner on the rearward face of the mounting body. The current transformers and current sensors can thus be adjusted conveniently during the production process. However, in order to ensure that the adjustment which has been carried out is maintained in all circumstances, it is recommended that it be possible to protect the adjustment elements against inadvertent operation by use of an access barrier, which can be fit once the adjustment process has been carried out. In this case, an encapsulation compound which covers each of the adjustment elements is particularly suitable for use as the access barrier.
As already mentioned, the current detection devices in a low-voltage circuit breaker provide output variables which are processed in a tripping device. The auxiliary energy which is required for operation of such a tripping device is generally likewise obtained from the electrical conductors of the circuit breaker by a current transformer. In this case, it has frequently been found to be expedient to provide a separate current transformer, which is independent of the described current detection devices, in order to provide the auxiliary energy. In this context, it is already known for a current sensor which is provided only for measurement purposes, and for an inductive current transformer, which is used to provide auxiliary energy, to be arranged in a common enclosure. For the purposes of an embodiment of the invention, this method of construction can also be used in a multi-pole mounting body, in such a way that a least one separate current transformer, which is used for supplying power, is arranged on the common mounting body.